High adhesion metallizing compositions

ABSTRACT

METALLIZING COMPOSITIONS COMPRISING NOBLE METAL (S) AND, IN PARTICULAR, INORGANIC BINDER WHICH CONTAINS A GLASS COMPOSED KOF 30-50% PBO, 30-40% SIO2, 2-8% AL2O3, 2-8% B2O3, 2-15% CAL, 0.5-5% TIO2 AND ZRO2. THESE COMPOSITIONS ARE APPLIED TO A DIELECTRIC SUBSTRATE AND USED IN THE ELECTRONIC INDUSTRY TO FORM HIGHLY DENSE FILMS WHICH EXHIBIT GOOD SOLDERABILITY, GOOD SOLDER LEACH RESISTANCE, GOOD INITIAL ADHESION AND GOOD THERMAL AGED ADHESION.

3,827,891 HIGH ADHESION METALLIZING COMPOSITIONS John R. Larry,Wilmington, Del. (396 Dansworth Road, Youngstown, N.Y. 14174) NoDrawing. Continuation of application Ser. No.

186,383, Oct. 4, 1971, which is a continuation-inpart of applicationSer. No. 146,799, May 25, 1971, which in turn is a continuation-in-partof application Ser. No. 99,318, Dec. 17, 1970, all now abandoned. Thisapplication June 11, 1973, Ser. No. 369,116

Int. Cl. C09d 5/24 US. Cl. 106-1 10 Claims ABSTRACT OF THE DISCLOSUREMetallizing compositions comprising noble metal(s) and, in particular,inorganic binder which contains a glass composed of 30-50% PbO, 30-40%SiO 28% A1 28% B 0 215% CaO, 0.5% TiO and ZrO These compositions areapplied to a dielectric substrate and used in the electronic industry toform highly dense films which exhibit good solderability, good solderleach resistance, good initial adhesion and good thermal aged adhesion.

CROSS-REFERENCE TO RELATED APPLICATIONS This application is acontinuation of Ser. No. 186,383, filed Oct. 4, 1971, which is acontinuation-in-part of Ser. No. 146,799, filed May 25, 1971, which inturn is a continuation-in-part of Ser. No. 99,318, filed Dec. 17, 1970,all assigned to the assignee of the present invention and now abandoned.

BACKGROUND OF THE INVENTION Modern electronic circuitry emphasizescompactness of component assemblies, to which metallizing compositionsare an important adjunct. Small assemblies of electronic components arefastened to a ceramic plate, or substrate, and interconnected by meansof electrode or conductor lines printed and fired onto the ceramicsubstrate. Such printed conductors should be mechanically strong andresistant to thermal shock and atmospheric contaminants. Of particularimportance are noble metalcontaining metallizing compositions andelectrodes therefrom. An essential advantage conferred by the noblemetal metallizing composition over ordinary, non-noble metalcompositions is the capability to be fired in air at high temperatureswithout being oxidized, thereby retaining good electrical conductivitywhile maintaining surface that can be wet by molten solder or brazingalloys.

Metallizing compositions normally contain, in addition to noble metals,an inorganic binder. The inorganic binder functions primarily to bindtogether the particulate noble metal andalso to cause the metal toadhere to the ceramic substrate. The binder is usually a powdered glassand the nature of the glass has significant effects on the overallproperties of the fired metallizing composition. There is a considerableneed for metallizing compositions which can be used for high performanceapplications. More specifically, metallizing compositions which yielddense fired films and which exhibit good solderability, gOOd solderleach resistance, good initial adhesion and good thermal aged adhesionare in constant demand by the electronic industry.

SUMMARY OF THE INVENTION This invention relates to novel glasses for usein metallizing compositions comprising, in weight percent, 30-50% PbO,30-40% SiO 2-20% CaO, 28% A1 0 28% B 0 0.5-5 TiO and 0.55% ZrO Themetallizing compositions of this invention comprise 60-98% nited StatesPatent O 3,827,891 Patented Aug. 6, 1974 finely divided noble metal and2-40% finely divided inorganic binder, wherein said binder contains theabovedescribed glass. These metallizing compositions possess a goodcombination of all of the desirable properties mentioned above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS TABLE I Weight percent OperablePreferred The above combination of metal oxides in the above proportionswere necessary to produce inorganic binders which are useful in highlyadherent metallizing compositions which produce fired metallizationshaving the previously described desirable properties. It is pointed outthat the inorganic binder may comprise, in addition to theabove-described glass, glass wetting agents such as bismuth oxide.

All of the noble metal and inorganic binder components should generallybe in a finely divided or powder form, i.e., in the form of powderssufficiently finely divided to pass through a 325 mesh (Standard SieveScale) stencil screen, said powder having particles no larger than about40 microns. Generally, the average particle size of the metal will rangefrom 0.1-5 microns while an average particle size range of 1 to 15microns for the inorganic binder is preferred.

The inorganic bindenmetal ratio has an effect on the conductivity, theadhesion and the surface properties of the ultimate metal films. As theproportionate amount of binder increases, the adhesion also increases;but the conductivity and surface wettability decrease in the films. Theproper balance must be maintained between the conductivity, adhesion andsurface properties. The metallizing compositions of this inventionshould contain from 60-98%, by weight, finely divided noble metal and,correspondingly, from 2-40% by weight finely divided inorganic binder.At least 2% inorganic binder is necessary to provide adequate adhesionof the metallizing composition to the substrate. On the other hand, theuse of more than 40% by weight inorganic binder provides films which donot accept solder readily.

The metallizing compositions of the invention will generally, althoughnot necessarily, be dispersed in an inert liquid vehicle to form a paintor paste for application to the dielectric substrate. The proportion ofthe metallizing compositionzvehicle may vary considerably depending uponthe manner in which the paint or paste is to be applied and the kind ofvehicle used. Generally, from 1 to 20 parts by weight of metallizingcomposition (metals, inorganic binder, etc.) per part by weight ofvehicle will be used to produce a paint or paste of the desiredconsistency. Preferably 3 to 10 parts of metallizing composition perpart of vehicle will be used.

3 4 Any liquid, preferably inert, may be employed as the for mostapplications. Useful results are obtained from vehicle. Water or any oneof various organic liquids with the invention with the other noblemetals as well, includor without thickening and/r stabilizing agentsand/or ing gold, silver, and gold-silver alloys. other common additives,may be utilized as the vehicle. The results of the tests described aboveare set forth Examples of organic liquids that can be used are the inTable III for Examples 1-3 which used glasses A-C, higher alcohols, suchas decanol; esters of the lower al respectively (see Table II).

cohols, for example, the acetates and propionates; the TABLE H terpenes,such as pine oil, alphaand beta-terpineol and the like; and solutions ofresins, such as the polymeth- A B c acrylates of lower alcohols, orsolutions of ethyl cellu- 45.3 40 35 lose, in solvents such as pine oil.The vehicles of U.S. 2-3 2 2 3,536,508 may also be utilized. The vehiclemay contain 410 5 5 or be composed of volatile liquids to promote fastseti g ting after application; or it may contain waxes, thermo- .7 2. 55 plastic resins, or like materials which are thermofiuid so TABLE IIIAdhesion (lbs.)

Fired 850 C. Fired 900 0. Fired 950 C. Solder leach Example GlassSolderabllity resistance Init. Aged Init. Aged Init. Aged 1 A Excellentcycles 13.9 14.4 12.7 14.3 11.3 1115 IIII:IIIIIIIIIIIIIIIIIIIIIIIIIIthat the composition may be applied at an elevated tem- 25 EXAMPLE 4perature to a relatively cold ceramic substrate upon which th iti t i dit l A metalllzlng composition comprising 80% finely d1- The metallizingcompositions are conventionally made Vided noble metals Palladium and51% Silver) and by admixing the metal(s) and inorganic binder solids in20% inorg hinder z s and 11% of glass the proportions of 60-98% and2-40%, respectively, Was dispersed in a liquid vehicle at a weight ratioof based on their total combined weight. Additionally, one approximatelyMore p y. the ingredients Were part of an inert liquid vehicle for every1 to 20 parts of Provided in the following Percentages y weight: 22-22%solids mentioned above may be admixed. Then the metal- Palladium, 40-44%Silver, 53-88% glass, 742% bismuth lizing composition is applied to adielectric ceramic sub- OXide, and the der Or 2 .98% inert vehicle. Thestrate and fired to form a conductive film. The invention procedures ofExarnple l were followed except that the is illustrated by the followingexamples. In the examples printed ta zeti s w re 111 the form of .13 xl3 crn. and elsewhere in the specification, all parts, percentage padsand the firing temperature was 850 C. The initial and proportions ofmaterials or components are by weight. edhesloh was and after 48 hoursVarious glass compositions, listed in Table II, were prethe agedhdheslell was The soldefablhty and the pared in frit form by melting therespective batch com- Solder leach resistance of 9 eY e w eonslflel'edgoodpositions and pouring the homogeneous melt into water. Prior to thePresent lhvehhohi lmtlal adhesloh of Over The fritted products were thenground to fine powders would have been qulte good, but the aged withparticle size ranging from 01-10 microns. Metalheslon would often go ofle lizing compositions were then prepared by admixing 87% 111 Contrast,a metalllllhg composlhen of the P aft fin l i id d bl metals gold, 13%platinum was prepared and tested in exactly the same manner as 3%palladium) and 3% inorganic binder 6% i g described above. Thernetallizing composition comprised and 7% glass from Table I). Binarygold-platinum and 86% fihely divided noble metal P h and gold-palladiumalloys would give essentially equivalent 56% f and 14% finely dividedlhqrganle bmder results for the purposes of this invention. Themetalliz- 2 3 and 4% of glass eonslshhg 0f ing compositions were thendispersed in a liquid vehicle Z110 214% 2 3 235% 2, 64% 2 3, z zconsisting of 10% ethyl cellulose and 90% beta-terpinol g cao N320) f ofat a ratio of approximately 4:1. These compositions were sohfls toliquid was llp y lhlhal then screen printed onto ceramic substrates (2.5cm. heslon was the aged edhesloh pp t0 square) through a patternedZOO-mesh screen having 16 The soldefablhty was considered good and theopenings with dimensions of .25 cm. by .25 cm. The Solder leachreslstance was 4 cyclesprints were dried and fired in a belt furnace atpeak tem- I claim: I

peratures ranging from 850-950 C. The fired chips were In F meballlzlngcQIIIPOSIUOII e p t0 be fired dip soldered in 62 311/36 Pb/Z Ag solder.Tinned cop- F a dleleqtyw substrate to p h y adherent films. per wireswere dip soldered onto the printed metalliz- 531d cofhlfosltloneompflslng, 1H welght P ing compositions which were in the form of .25cm. by 60 finely dlvlded noble P n f 240% finely dlltlded 15 padsinorganic glass frlt binder, the improvement comprising The adhesion wasmeasured by pulling the soldered as said binder, a glass consistingessentially of:

leads with Chatillon tester. Accelerated aging tests were Percent y gconducted by keeping the soldered chip with lead attach P 3 :4 ments at125 C. for 100 hours prior to determining the 65 2 2?) bond strength.Solder leach resistance was assessed by using the following test: Afired sample containing a .055 A1203 cm. wide line was fluxed and dipsoldered in a 60 Sn/ 36 Pb/Z Ag solder for 10 seconds, allowed 2-3seconds for T102 solder leveling, and quenched in trichloroethylene.This ZIOZ 0-5-5 cycle was repeated until the .055 cm. line leachedthrough or until 25 cycles were passed at which time the test was 2. Acomposition in accordance with Claim 1 wherein terminated. Such binaryand ternary gold-platinum-pal- Bi O in admixture with said glass.

ladium compositions which pass 15 cycles and exhibited 3. A compositionin accordance with Claim 1 wherein adhesion values of 6-8 lbs. aregenerally quite acceptable the noble metal comprises platinum, palladiumand gold.

4. A composition in accordance with Claim 1 wherein the noble metalcomprises platinum and gold.

5. A composition in accordance with Claim 1 wherein the noble metalcomprises palladium and gold.

6. A composition in accordance with Claim 1 wherein the noble metalcomprises palladium and silver.

7. A composition in accordance with Claim 1 wherein the noble metalcomprises at least one of gold and silver.

8. A composition in accordance with Claim 1 wherein said glass consistsof 40-50% PbO, 32-38% 5102, 5-15 CaO, 3-6% A1 0 3-6% B 0 0.54% TiO and(LS-4% Zr0 9. A paste composition comprising the metallizing compositionof Claim 2 dispersed in an inert liquid vehicle.

10. A dielectric substrate having the metallizing composition of Claim 1in firmly adherent relationship thereto.

References Cited LORENZO B. HAYES, Primary Examiner US. Cl. X.R.

